From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760631AbXG3IAi (ORCPT ); Mon, 30 Jul 2007 04:00:38 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755355AbXG3IAb (ORCPT ); Mon, 30 Jul 2007 04:00:31 -0400 Received: from smtp4-g19.free.fr ([212.27.42.30]:40763 "EHLO smtp4-g19.free.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753565AbXG3IAa (ORCPT ); Mon, 30 Jul 2007 04:00:30 -0400 Message-ID: <46AD9A74.8070302@free.fr> Date: Mon, 30 Jul 2007 09:59:48 +0200 From: John Sigler User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.0.8) Gecko/20061108 SeaMonkey/1.0.6 MIME-Version: 1.0 To: linux-kernel@vger.kernel.org, linux-rt-users CC: johnstul@us.ibm.com, tglx@linutronix.de Subject: Re: System clock frequency offset changes drastically across reboots References: <46A9DD7A.80104@free.fr> In-Reply-To: <46A9DD7A.80104@free.fr> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org [ Expanding recipients list ] John Sigler wrote: > I'm using 2.6.20.7-rt8 on a P3. But some ntpd users have reported the problem with mainline kernels and different versions. > I've noticed that the frequency offset of my system clock (computed > either by ntpd, or by hand) changes drastically across reboots. > > By drastically, I mean +/- 60 ppm every time I reboot. > > Apparently this is caused by some imprecision in the frequency > estimation done in calculate_cpu_khz() (arch/i386/kernel/tsc.c) > > My brutally crude work-around was to skip the computation altogether and > hard-code the "correct" value for cpu_khz. > > http://linux.kernel.free.fr/cpu_khz.adlink > > Has this issue been investigated more thoroughly by other users? Regards.